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give C struct to assembler...

Etienne SOBOLE
Note: This was originally posted on 24th November 2011 at http://forums.arm.com

how can I send the offset of a C struct to en assembly code ? For example

In my C code I have

typedef struct
{
  unsigned int a;
  unsigned int b;
} CMyStruct;
I send to an ASM function a pointer of a CMyStruct structure Let suppose that my pointer is into R0

To access to a and b attribute I need to do that.

ldr      r1, [r0, #0] // read a
ldr      r2, [r0, #4] // read b
Is there anyway to not specify #0 and #4 as contant value ? Something like

ldr      r1, [r0, CMyStruct.a] // read a
ldr      r2, [r0, CMyStruct.b] // read b
Thank's Etienne
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  • Note: This was originally posted on 26th November 2011 at http://forums.arm.com

    Inline assemble will work for this purpose.
    typedef struct{
            unsigned int a;
    unsigned int b;
    }MyStruct_t, *MyStruct_p;
    void pass_para_to_asm(MyStruct_t para)
    {
    __asm__ volatile("mov  %0, 0x0a\n"
         "mov %1, 0x0b\n"
         :
         :=r(para.a), =r(para.B)
         ;
         )
    }
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  • Note: This was originally posted on 26th November 2011 at http://forums.arm.com

    Inline assemble will work for this purpose.
    typedef struct{
            unsigned int a;
    unsigned int b;
    }MyStruct_t, *MyStruct_p;
    void pass_para_to_asm(MyStruct_t para)
    {
    __asm__ volatile("mov  %0, 0x0a\n"
         "mov %1, 0x0b\n"
         :
         :=r(para.a), =r(para.B)
         ;
         )
    }
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